Flush-back filters of this kind are preferably used for the filtration of fuels and lubricating oils. In the known flush-back filters, the cylindrical filter elements are grouped within the filter chamber in a circle around the filter axis and fixed to an apertured plate which divides off the filter chamber fitted with the filter outlet from the intake chamber fitted with the filter inlet on the fouled side of the filter. In the lower intake chamber, the flushing member is rotatably arranged around the filter axis, made up of a radial flushing arm, which for the performance of the flushing operation respectively overlaps with its opening a lower inlet opening of the filter elements, with the result that the respective filter element is cleaned by the filtrate flowing inwards from the outside (DE-OS No. 20 21 918, DE-OS No. 27 57 090, DE-GM No. 69 46 797, DE-OS No. 26 20 435). With these flush-back filters the flushing arm is gradually rotated further, something which is effected by means of a rotary drive mechanism seated on the filter housing or accommodated in the interior space between the filter elements arranged on one circle.
The known-flush-back filters are not free from disadvantages. The flush-back operation is carried out discontinuously with these filter appliances using quite large quantities of filtrate as flushing fluid. Upon changeover of the flushing arm, considerable pressure surges can occur within the conduit system. Besides this, the known flush-back filters are mostly relatively large in construction, something which is disadvantageous in the case of the confined mounting spaces often available. The flushing arm has a relatively large lever arm, thus making a large energy consumption necessary for its rotary motion. The known flush-back filters must be used together with a so-called safety filter, which is arranged in the oil circulation between the flush-back filter and the internal combustion engine, so that the former cleans the oil flowing to the internal combustion engine in the event of damage to the flush-back filter. The mesh width of the safety filter is generally two or four times larger than that of the filter elements of the flush-back filter.